The present invention generally relates to a magnetic recording and reproducing system such as a video tape recorder (VTR) and a digital audio tape recorder (DAT), in which a tapelike magnetic recording medium is wound around a rotary cylinder having a magnetic head mounted thereon so as to be fed therearound such that recording and reproduction of signals can be performed.
Initially, a known reel base braking mechanism is described. At a supply reel base, a tension regulating mechanism, a main brake mechanism, a soft brake mechanism and three control mechanism for controlling the tension regulating mechanism, the main brake mechanism and the soft brake mechanism, respectively independently of one another are required to be provided.
The tension regulating mechanism includes a pivotal tension arm having a tension post attached thereto, a tension band which is wound around the supply reel base and at least one end of which is attached to the tension arm and a spring member for imparting a moment to the tension arm. By optimizing back tension of a magnetic tape during its running, the tension regulating mechanism optimizes contact pressure of the magnetic tape relative to a rotary head mounted on a rotary cylinder.
The main brake mechanism includes an arm to which a block type brake shoe is attached and a spring member. At the time of stop of fast feed and rewinding of the magnetic tape, the main brake mechanism overcomes inertia of the supply reel having the magnetic tape wound therearound so as to stop rotation of the magnetic tape in a short period.
The soft brake mechanism includes an arm and a spring member. In order to prevent slack of the magnetic tape during loading of the magnetic tape, the soft brake mechanism depresses a tension band against the supply reel base so as to apply a small braking force to the supply reel base.
On the other hand, at a take-up reel base, a main brake mechanism having the same function and arrangement as those of the main brake mechanism provided at the supply reel base, a soft brake mechanism and two control mechanisms for controlling the main brake mechanism and the soft brake mechanism, respectively independently of each other are required to be provided. The soft brake mechanism at the take-up reel base includes an arm to which a block type brake shoe is fixed and a spring member and is designed to apply a small braking force to the take-up reel base so as to prevent slack of the magnetic tape at the time of loading or reverse reproduction of the magnetic tape.
Therefore, the number of components of the above mentioned mechanisms is quite large, thereby resulting in substantial rise of production cost of the known reel base braking mechanism. Meanwhile, since the many block type brake shoes are employed, braking force applied to the reel base is unstable and thus, the magnetic tape is readily damaged undesirably.
Then, a prior art tape cassette loading apparatus is described. In a conventional tape cassette loading apparatus of a type in which by using a pivotal arm (wiper arm), a tape cassette partially projecting out of the tape cassette loading apparatus is displaced substantially horizontally so as to be drawn into the tape cassette loading apparatus and then, is displaced vertically so as to be loaded at a predetermined position of the prior art tape cassette loading apparatus, speed reduction ratio from a DC motor acting as a driving source to the wire arm is constant. Therefore, in order to prevent increase of variations of driving load and feed rate of the magnetic tape between cassette loading for lowering the tape cassette vertically and cassette unloading for lifting the tape cassette vertically, a lever mechanism is required to be provided additionally. The lever mechanism includes an arm for not only hindering vertical descent of the tape cassette but promoting vertical ascent of the tape cassette and a spring member for applying an urging force to the arm. Therefore, production cost of the prior art tape cassette loading apparatus is raised due to increase of the number of its components and the number of its assembly steps.
Meanwhile, also in a speed reduction mechanism for driving the tape cassette loading apparatus which is constituted by the above mentioned DC motor, a plurality of gears, a main cam gear, a driving rack and the wiper arm, since a displacement angle of a worm gear mounted on an output shaft of the DC motor is set small, self-locking of the worm gear occurs. Hence, when the tape cassette projecting out of the tape cassette loading apparatus is pushed into the tape cassette loading apparatus, a spring member for defining the pushing force should be provided between the main cam gear and the wiper arm. In addition, a mechanism for detecting that the tape cassette has been pushed into the tape cassette loading apparatus and a detection means are required to be provided. As a result, production cost of the speed reduction mechanism is raised due to the number of its components.
Especially, the above mentioned detection means is required to be set to be detectable even when the power source is in OFF state. Therefore, in case an optical detection means is used as the detection means, the optical detection means should be subjected to on-off control so as to lengthen its service life and shorten period of its ON state. In this case, such a problem arises that response time from push of the tape cassette into the tape cassette loading apparatus to start of drawing of the tape cassette into the tape cassette loading apparatus is long.
Then, a conventional tape loading mechanism is described. An improved conventional tape loading mechanism includes a sector gear for driving a link mechanism for driving a tape guide and an operational mode switching means formed integrally with a rack. The sector gear and the operational mode switching means are provided on a lower face of a chassis such that the sector gear is rotationally driven by displacing the operational mode switching means. A regulation member is required to be provided for regulating rotation of the sector gear even if the operational mode switching means is further displaced upon completion of tape loading for the purpose of switching operational mode of a magnetic recording and reproducing system. Thus, such a drawback is incurred that the operational mode switching means is made larger in size. Furthermore, the improved conventional tape loading mechanism cannot be structurally applied to a reel base driving mechanism of a so-called "in-cassette" type in which a capstan is provided in a cassette mouth and the number of its components can be minimized, thereby resulting in restraints on design of the magnetic recording and reproducing system.